In its most widespread form, a tap is a tool whose periphery is threaded in interrupted manner, thus defining cutters which act by removing matter and more particularly by removing turnings.
This method of tapping by removal of turnings presents drawbacks due to its basic design, as the removal of turnings cuts the fibers of the metal and results in threads whose resistance is often judged insufficient.
This is why another form of tapping is currently preferred, which acts by deformation of matter, therefore without prohibitively injuring the metal.
Taps are in that case taps of polygonal section. When the tap rotatingly penetrates in the hole to be tapped, it is the apices of the polygon which deform the matter in order to produce the desired threading.
The process of tapping by deformation is therefore considered at the present time as the only process valid for obtaining threads which are highly resistant and therefore reliable and long-lasting.
Presently known taps employing deformation, i.e. taps of polygonal section, are subjected, when they act to deform the matter, to great friction generated by the considerable efforts which necessarily come into play. This results in considerable heating and wear of the tap and consequently a relatively short life therefor.
In addition, the work speeds of these taps are necessarily relatively slow, which penalizes industrial productivity when these taps are intended to equip automatic tappers such as the one described in document EP-A-0 192 586 in the name of the Applicants.
It is an object of the present invention to overcome these drawbacks of the taps acting by deformation as presently used in the state of the art.